Food patties of various kinds, including hamburgers, molded "steaks", fish cakes, chicken patties, pork patties, potato patties, and others, are frequently formed in high-volume automated molding machines. Patty molding machines that can be successfully adapted to any of these food products are described in U.S. Pat. Nos. 3,887,964 to L. R. Richards, 4,054,967 to G. A. Sandberg et al, and 4,182,003 to LaMartino et al. A smaller machine is described in Sandberg U.S. patent application Ser. No. 106,249, filed Oct. 7, 1987. In all of these machines, using relatively small fill passages, the fill passage is always effectively sealed off from the space outside of the molding station.
Although any of these machines, and others, can produce food patties of consistent size, weight, and configuration, substantial problems and difficulties may remain. Thus, in many patty molding machines it may be difficult to duplicate the texture of hand-molded hamburgers and other such patties. Machine-molded food patties may tend toward excess shrinkage when cooked. Distortion in the patty shape may also occur when the patties are cooked.
Machines for molding food patties that have essentially uniform texture and minimal shrinkage when cooked are disclosed in Sandberg et al U.S. Pat. No. 4,356,595; the patties also hold their shape consistently following cooking. In those patty molding machines a multi-orifice plate is interposed in the outlet end of a fill passage extending from a food pump to a cyclically reciprocating mold plate. The food pump is preferably controlled so that the maximum fill pressure, desirable for consistent filling of the mold cavities, is used for only a limited part of each mold plate cycle.
Those machines, while highly satisfactory for many food products (e.g., ground pork, ground chicken, finely ground beef, etc.) are not entirely successful for some other foods, particularly foods that incorporate long and sometimes tough fibers. One such food product is coarsely ground beef. A food product of this nature tends to create an excessive buildup of fibrous material at the entrances of the orifices, requiring an excessive pumping pressure to operate the patty molding machine at high speeds. That buildup problem is effectively solved in the molding machines described in Sandberg U.S. Pat. No. 4,372,008, using a stripper plate slidably mounted immediately adjacent the fill plate; the stripper plate has fill openings that align one-for-one with the fill plate orifices when the stripper plate is in a fill location. Once the mold cavities are filled, the stripper plate slides transversely of the direction of mold plate movement to cut food fibers on the upstream side of the fill plate.
Molding machines using wide-area fill passages with multi-orifice fill plates have had one distinct disadvantage; there has been no convenient and effective way to maintain a seal-off of the mold cavity and feed passage throughout the mold plate cycle. Thus, as the mold plate moves out toward its discharge (knockout) position, there is a portion of the cycle time when continuous paths are open from the feed passage, through some of the stripper plate fill openings and feed plate fill orifices, and through the mold cavity, to the space outside of the molding station. Even if these paths are quite small, the results are highly undesirable; waste of the food product, distortion of the patties, violation of sanitary requirements, and reduced pumping efficiency can all occur.
Previous efforts to resolve this lack of an effective seal-off, in large area multi-orifice fill passage machines, have included controls to shut off the food pump completely during the times in each mold cycle when continuous paths to the space around the mold station are present. This expedient is difficult to implement and not particularly effective. Another technique that could be used for effective seal-off would be to extend the housing of the molding station (e.g., the mold plate support and its cover) far enough in the direction of mold plate movement toward its discharge station to achieve full seal-off. But this is quite uneconomical; it requires a major machine re-design and inherently increases the mold plate cycle time and machine size and cost.